The invention relates to a method of monitoring the progress of an oxidation-type sterilization process and a chemical indicator therefor, in particular an ozone sterilization process.
Sterilization is important in many fields, especially in medicine. One means of sterilization uses ozone gas as a sterilizing agent. One such method for sterilizing medical instruments uses a sealed device such as the TSO3-125L (available from TSO3). The effectiveness of ozone increases with increased humidity and therefore, with humidified ozone, sterilization can be effected at low temperatures, even at room temperature. This reduces the need for high temperature apparatus and permits use of less ozone. Using lower temperatures is also an advantage since ozone is temperature sensitive and decomposes rapidly at higher temperatures.
Naturally, it is important to be able to monitor a sterilization procedure to verify that sterilization has been effective.
Conventionally, sterilization can be verified by placing indicators in the sterilization chamber with the medical instruments load. Chemical and biological indicators are both used to monitor sterilization. A chemical indicator is designed to provide a characteristic color change in response to one or more of the physical conditions within the sterilizing chamber. Chemical indicators are often integrated with other sterilization verification devices to provide additional evidence of exposure to sterilant. Biological indicators are composed of strips containing a high number of micro-organisms. After sterilization is complete, the strip is cultured to see if all the micro-organisms have been killed. If the sterilization is successful, no growth will be observed. Such procedures are generally required by local health and safety regulations.
If this were the only means of verifying adequate sterilization, the articles sterilized could not be used for at least 24 hours. This imposes inconvenient storage or inventory requirements which may not be possible, for example, in some hospitals. Therefore there is a need for a means to monitor the sterilization more quickly.
Chemical indicator performance is explained in more detail in Volume 1.3 Sterilization Part 3 Industrial Process Control of the Association for the Advancement of Medical Instrumentation (AAMI) Standard Recommended Practice and American Standard Institute (ANSI).
U.S. Pat. No. 5,518,927 (Malchesky et al) discloses an indicator compound. However, the compounds disclosed are unstable and change colour over time, especially when exposed to light, and therefore they are not reliable. Further, they are not suitable, for some oxidation-type sterilants. For example, for ozone, they change colour even when the ozone is dry and non-sterilizing. Also, dyes taught in this reference, are carcinogenic.
It is an object of the present invention to provide a means to monitor sterilization in an oxidation-type sterilization process, particularly an ozone sterilization process.
According to the present invention there is provided a method of monitoring a sterilization process having an oxidation-type sterilant, said process comprising the steps of:
providing an indicator compound capable of exhibiting a colour change upon exposure to the sterilant, the indicator compound being free of heterocyclic nitrogen, diazo nitrogen and amino nitrogen, and selected from the group consisting of anthraquinone dyes, triarylmethane dyes and xanthene dyes;
exposing the indicator compound to the sterilization process; and
observing the compound for a change of colour.
According to another aspect of the present invention there is provided an indicator for an ozone sterilization process comprising an ozone indicator compound and a substrate.
According to another aspect of the present invention there is provided a use of an ozone indicator compound in the manufacture of an indicator for a sterilization process having humidified ozone as the sterilant.